A carbon fiber-reinforced composite material has been widely utilized for structural materials of aircrafts, automobiles, and the like, or for applications in general industries, sports, or the like, such as tennis racket, golf shaft and fishing rod, by making use of its high specific strength and high specific elasticity. The form of the carbon fiber used therefor includes a woven fabric made from continuous fibers, a UD sheet composed of unidirectionally arranged fibers, a random sheet made from cut fibers (discontinuous fibers), a nonwoven fabric, or the like.
In recent years, a composite material using, as a matrix, a thermoplastic resin instead of the conventional thermosetting resin is attracting attention. For example, there has been developed a molding method where a molding material impregnated with a discontinuous carbon fiber and a thermoplastic resin is heated to not less than the softening point (plasticization temperature) of the thermoplastic resin, charged into a mold adjusted to not more than the melting point or not more than the glass transition temperature, and then shaped by mold clamping (Patent Documents 1 and 2).
Patent Document 1 describes a molded product having a smooth surface and a uniform thickness, which is obtained by press-molding an easily flowable molding material containing a discontinuous carbon fiber in a specific form and a thermoplastic resin, and a manufacturing method thereof.
Patent Document 2 has proposed a technique for manufacturing a complicatedly shaped or large-size molded product by applying low-pressure molding and thereby allowing the flow of a molding material containing a discontinuous carbon fiber and a thermoplastic resin so as to prevent an increase in the capacity of a molding machine or utility equipment.
Patent Document 3 describes a method for obtaining a molded product with excellent surface transferability and good surface appearance by controlling the acceleration region from the start of pressing of a molten thermoplastic resin until the compression rate reaches a maximum rate.